In the prior art, the teaching particularly of model USD206402 is known and describes a reinforced nut with a frustoconical collar, represented in a schematic manner in FIGS. 1A and 1B.
FIG. 1A represents a front view of such a nut 1 and FIG. 1B represents a side view with a partial cross-section of the same nut 1. The cross-section is defined by planes 1B-1B. The nut 1 comprises a shank 2 and a frustoconical collar 3. A cylindrical inner wall 4 of the nut 1 is threaded and may have a recess. Six buttresses 5 connect the collar 3 to the shank 2.
In the prior art, non-reinforced nuts with frustoconical collars are also known, such as those represented in FIGS. 2A and 2B. The same types of geometries are found with regard to the screw heads.
FIG. 2A represents in a schematic manner an oblique perspective view of an example of a forged nut 5 with a frustoconical collar 6. A junction between a hexagonal shank 7 and the frustoconical collar 6 of the forged nut 5 comprises a fillet present in the form of an elliptical rim 8. A circular base 9 of the cone of the collar 6 extends into a cylinder 10. When a wrench socket, not represented, is threaded around the shank 7, one end of the socket abuts against the elliptical rim 8. A height 11, separating a crest 12 of the elliptical rim from an upper surface 13 of the forged nut 5, is effectively in contact with the wrench socket during a tightening or loosening operation of the forged nut 5; this is the wrenching height or useful height 11. The cylindrical inner wall 4 of the forged nut 5 is threaded and may have a recess.
FIG. 2B represents in a schematic manner an oblique perspective view of an example of a machined nut 14 with a frustoconical collar 15. A junction 16 between a hexagonal shank 17 and the frustoconical collar 15 of the machined nut 14 is machined so as to form a fin and so that the shank 17 has perfectly rectangular sides. A circular base 18 of the cone of the collar 15 extends into a cylinder 19. When a wrench socket, not represented, is threaded around the shank 17, one end of the socket abuts against the junctions 16. A useful height 20, separating a junction 16 from an upper surface 21 of the machined nut 14, is effectively in contact with the wrench socket during a tightening or loosening operation of the machined nut 14. The cylindrical inner wall 4 of the machined nut 14 is threaded and may have a recess.
For nuts with identical dimensions, the useful height 11 of the forged nut 5 is therefore shallower than the useful height 20 of the machined nut 14. Due to the elliptical rims 8, the support surface with the appropriate wrench socket is less significant, which reduces the transmissible torque.
FIG. 2C schematically represents a side view of half of a forged nut 5 with a frustoconical collar 6 and half of a machined nut 14 with a frustoconical collar 15 from the prior art. This figure shows, for the same overall height 22, collars 15 and 6 to be different and the wrenching height 20 to be identical. In particular, the cylindrical part 10 is shallower than the cylindrical part 19.
FIG. 2D schematically represents a side view of half of a forged nut 5 with a frustoconical collar 6 and half of a machined nut 14 with a frustoconical collar 15 from the prior art. This figure shows collars 15 and 6 to be identical and the wrenching height 11 of the forged nut 5 to be shallower than that 20 of the machined nut 14.
It has become apparent that the dimensions of the collar nuts of the same nominal size, i.e. of the same inner threading, may vary according to the method of manufacture. This also applies for all driving means such as screw heads. This is why, in the following text, it must be remembered that the invention relates to all driving means with an inbuilt collar.
It is initially advised that, if the useful wrenching height is to be kept the same for both a forged driving means and a machined driving means, the height of the shank must be increased by a length equal to the height of a rim, the total height of the driving means therefore being increased to the same extent.
This heterogeneity of shank heights for driving means intended for the same use is a source of numerous technical problems.
Indeed, as the shank height of a forged driving means is greater than that of a shank of a machined driving means, the forged driving means have a greater volume, therefore a greater mass and more material, which is problematic and costly with regard to their storage, transport and use, in particular in aircraft.
If, on the other hand, the height of the collar is reduced, this reduction is detrimental to the mechanical aspect, i.e. the strength of the collar.
Finally, as the forged driving means are generally produced in large quantities compared to the machined driving means, the aforementioned problems are all the more incapacitating.
On the machined version, numerous fins can be observed in a transition zone between the hexagonal socket faces and the collar. These fins originating from the machining process are not suited to forging. Indeed, identical angular shapes cannot be forged as this creates material filling problems. Furthermore, for the forged version, elliptical fillets replace the machining fins to ease the filling of a die with the chosen material such as a titanium alloy, stainless steel, nickel alloy or even an aluminium alloy.
It therefore follows that, for the same wrenching height and the same height of the driving means, the machined driving means and the forged driving means do not have the same collar height. The collar strength is therefore weaker on a forged driving means.
In order to produce equal levels of strength between the machined collar and the forged collar, either the height of the forged driving means must be increased, which has the disadvantage of making it heavier than the machined driving means, or the wrenching height reduced, which reduces the transmissible torque for tightening and loosening operations.